🚀 go-pugleaf

I am looking for some clarification on when (and where) the re-writing
rulesets 1 and 2 are invoked.
The comments in the sendmail.cf files indicate that they are:
S1:	"Sender Field Pre-rewriting" and 
S2:	"Recipient Field Pre-rewriting".
As far as I can tell from actual experience and looking at the source
code, this corresponds to sendmail on a given machine rewriting the
sender's address (the "From:" field) with ruleset 1, and the recipient's
address (the "To:" and "Cc:" fields) with ruleset 2.  

However, in EVERY diagram of the semantics of sendmail rewriting rules that I
have seen, the rules go something like this:

To:/Cc: ---->3---->D---->1---->S---->4---->To:/Cc:
                         ^

From:   ---->3---->D---->2---->R---->4---->From:
                         ^

which to me looks like sendmail rewrites the "To:" and "Cc:" fields using
ruleset 1, and the "From:" gets rewritten with ruleset 2.  What gives?  Am I
missing something obvious, or is the diagram incorrect? 
----------------------------------------------------------------------------
Douglas Neuhauser		Div. of Geological and Planetary Sciences
doug@seismo.gps.caltech.edu	California Institute of Technology
818-356-3993			MS 252-21, Pasadena, CA  91125